Mobile radios mounted in cars, motorcycles, trucks or other vehicles are powered by the vehicle's main power supply. A main power supply line is run throughout the vehicle to power electromechanical components in addition to the mobile radio. The main power supply line is often subjected to unwanted noise, commonly referred to as power supply ripple or alternator whine. The intensity of alternator induced radio noise increases and decreases with changes in engine speed. The noise may also be caused by the noisy electrical and thermal environment in the vehicle.
Conventional approaches to addressing unwanted noise on the supply line include the use of ripple regulators. These ripple regulators utilize capacitors, inductors and transistors for forming passive filters that block the ripple noise on the supply line. However, the low-frequency filter bandwidth required for these filters can only be realized by the use of large capacitors and inductors. This makes these approaches undesirable for applications where size and/or weight are important factors. Furthermore, the parasitic capacitance and inductance of transistors leads to timing delays in the components of the regulator. As a result, the output of the regulator may overshoot or undershoot the desired output. Heating of capacitors and inductors is another cause of concern in such regulators.
Other approaches to overcome the power supply noise problem have required significant hardware additions that draw additional current and may result in a voltage drop on the power supply line. Feedback control techniques that have been used in the past tend to introduce the potential for instability and oscillation, thereby putting more noise on the power supply line.
Accordingly, it would be desirable to have an improved method and apparatus to address unwanted noise on the power supply line, particularly as applied to powering a mobile radio in a vehicular environment. It would be further desirable to have an improved method and apparatus with reduced power requirement.
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